This invention is related to U.S. patent application Ser. No. 09/009,759 filed Jan. 20, 1998 of Charles D. Melville for Augmented Imaging Using A Silhouette To Improve Contrast. This invention also is related to U.S. patent application Ser. No. 09/188,991 filed Nov. 9, 1998 of Charles D. Melville et al. for Method and Apparatus for Scanning Optical Distance. The content of all such applications are incorporated herein by reference and made a part hereof.
This invention relates to scanning beam display devices, and more particularly to optical configurations for scanning beam display devices.
A scanning beam display device is an optical device for generating an image that can be perceived by a viewer""s eye. Light is emitted from a light source, collimated through a lens, then passed through a scanning device. The scanning device defines a scanning pattern for the light. The scanned light converges to focus points of an intermediate image plane. As the scanning occurs, the focus point moves along the image plane (e.g., in a raster scanning pattern). The light then diverges beyond the plane. An eyepiece is positioned along the light path beyond the intermediate image plane at some desired focal length. An xe2x80x9cexit pupilxe2x80x9d occurs shortly beyond the eyepiece in an area where a viewer""s eye is to be positioned.
A viewer looks into the eyepiece to view an image. The eyepiece receives light that is being deflected along a raster pattern. Light thus impinges on the viewer""s eye pupil at differing angles at different times during the scanning cycle. This range of angles determines the size of the field of view perceived by the viewer. Modulation of the light during the scanning cycle determines the content of the image.
For a see-through display, a user sees the real world environment around the user, plus the added image of the scanning beam display device projected onto the retina. When the user looks at an object in the field of view, the eye performs three basic functions. For one function, each eye moves so that the object appears at the center of vision. For a second function, each eye adjusts for the amount of light coming into the eye by changing the diameter of the iris opening. For a third function, each eye focuses by changing the curvature of the eye lens. If the focal distance from the third function does not match the distance to the point of convergence, then the brain detects a conflict. Nausea may occur.
According to the invention, a more lifelike image is generated with a virtual retinal display by including a method and apparatus of variable accommodation.
According to one aspect of the invention, the scanning beam display device controls the curvature of scanning light waves impinging on the eye to simulate image points of differing depth. Images at far distances out to infinity have flat light waves impinging the eye. Images at near distances have convex-shaped light waves impinging the eye. Thus, to simulate an object at a far distance the light waves transmitted from the display to the eye are flat. To simulate closer objects, the light wave curvature increases. The eye responds to the changing curvature of the light waves by altering its focus. The curvature of the generated light waves relates to a desired, xe2x80x98apparent distancexe2x80x99 between a virtual object and the eye.
According to another aspect of the invention, a variable focus lens is included in the virtual retinal display to alter the shape of the light waves. The lens varies its focal length over time as desired. For example, for an image that is 640 by 480 pixels, there are 307,200 image elements. The variable focus lens is able to adjust its focal length fast enough to define a different focal length for each image element.
According to another aspect of the invention the variable focus lens is formed by a resonant crystalline quartz lens. The resonant lens changes thickness along its optical axis, thus varying its focal length. The lens varies in focal length with respect to time. By varying the time when a light pulse enters the resonant lens, the focus is varied. A non-resonant lens is used in another embodiment where its response time is fast enough to focus for each image element.
According to another aspect of the invention, a device which changes its index of refraction over time is used instead of a variable focus lens. In one embodiment an acousto-optical device (AOD) or an electro-optical device (EOD) is used. In the AOD, acoustic energy is launched into an acousto-optic material to control the index of refraction of the AOD. In one embodiment of an EOD, a lens is coated with a lithium niobate layer. An electric field is applied across the lithium niobate material to vary the index of refraction of the coating. Changing the index of refraction changes the effective focal length of the lens to vary the focus distance of the virtual image.
In another embodiment an optical device changes its index of refraction based upon the intensity (frequency) of an impinging infrared beam. The current intensity of the infrared beam in effect sets the current index of refraction for the device. Varying the intensity of the infrared beam varies the index of refraction to vary the effective focal length of the optical device.
Another embodiment includes a compressible, cylindrical gradient index lens as a focusing element. A cylindrical piezoelectric transducer compresses an outer shell of the gradient index cylinder. Compression of the cylinder shifts the physical location of the lens material to changes the index of refraction gradient, thereby changing the focal length. Another embodiment includes a current driven device that uses free-carrier injection or depletion to change its index of refraction.
According to another aspect of the invention, a variable focus lens serves to correct the curvature of the intermediate image plane for errors introduced by the scanners or from the aberration of other optical elements. In an exemplary embodiment, a aberration map of the system is stored in a look-up table in memory. The aberration map provides correction data for each image element. The correction data drives the variable focus element to adjust the focal depth for each image element.
According to another aspect of the invention, the light source is moved to vary the focal length instead of introducing a variable focus lens to vary the focal length.
According to another aspect of the invention, the light source emits light toward a mirror that reflects the light toward a lens of the display. The mirror is movable about an axis causing the angle of reflection to vary. A control signal determines the position of the mirror and thus the angle of reflection. As the angle of reflection varies, the focal distance of light exiting the lens varies proportionately.
According to another aspect of the invention, an augmented display includes variable accommodation. The scanning beam display is augmented to include a background image upon which a virtual image is augmented. An object within the virtual image is scanned to have an apparent distance within the field of view. Thus, a virtual object may be placed within a real world background view. The apparent distance is controlled by controlling the curvature of the light waves which scan the object pixels onto the viewer""s eye.
According to another aspect of the invention, distance of a background image object is measured and used to specify the apparent distance of a virtual object to be placed in proximity to such background image object.
According to another aspect of this invention, the intensity of a virtual image is controlled relative to measured intensity of a background image. As a result, the relative contrast between the virtual image and background image may be the same even within different background image intensities. Further, the virtual image intensity can be controlled to be approximately the same as the background image for a more realistic viewing effect.
One advantage of varying the curvature of light is that the produced image is more life-like, enhancing the user""s feeling of presence. These and other aspects and advantages of the invention will be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings.